Solar power for project

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RandyPfeifer
 
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Solar power for project

Post by RandyPfeifer »

Hi, I'm building a small project that uses 20-40ma (depending on display content). I want to drive it (an Arduino processor + a couple I2C devices) with a pair of 3.7v 620 mAh Lithium Polymer batteries in parallel connected to a "Adafruit Micro-Lipo Charger for LiPo/LiIon" for charging from a USB port. The system will operate in the field from the battery most of the time but will use the USB-C port to charge the battery and program the device. The system will be powered from the batteries via the BAT pin on the charger board.

Because the device will be in the field for weeks at a time, I would also like to add a 5V solar panel to the system in parallel with the 5V line on the USB-C port (upstream of the micro-Lipo Charger device) to charge the battery when out and about. Assuming sufficient sunlight, it should keep the battery charged for those cloudy days...


All make sense? Any reason this won't work just fine (assuming the sun shines when I need it).

Thanks in advance

Randy

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adafruit_support_bill
 
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Re: Solar power for project

Post by adafruit_support_bill »

You would be better off with a solar-specific charger like this one: https://www.adafruit.com/product/4755
The variable output of a solar panel disrupts the charge cycle of most simple charger controllers - resulting in terrible efficiency. The solar-specific charge controllers are designed to deal with the output characteristics of solar panels.

For more details, see:
https://learn.adafruit.com/adafruit-bq2 ... -3071654-4

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RandyPfeifer
 
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Re: Solar power for project

Post by RandyPfeifer »

Great. thanks for the quick response. I'll take a look at it.

Thanks again.

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sj_remington
 
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Re: Solar power for project

Post by sj_remington »

Any reason this won't work just fine (assuming the sun shines when I need it).
There is no good reason to assume that. It is much wiser to plan for the event that the sun does not shine when you need it.

Most people choose batteries with sufficient capacity to cover seasonally expected periods of bad weather and dark skies.

Then they choose a solar panel with high enough output current to charge the battery during a reasonable number of seasonally expected hours of direct sunlight.

Battery lifetime in hours can be easily estimated as (battery capacity in mAh)/(average current draw in mA). Derate the battery to take into account aging and manufacturers' tendency to exaggerate.

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RandyPfeifer
 
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Re: Solar power for project

Post by RandyPfeifer »

Thanks for your comments and insights.

the "assuming the sun shines" part was a bit of a joke. I have calculated expected life of the product without sunshine. I don't want to bring a giant battery (physical bulk and weight concerns in a wilderness environment). It's not an essential service so having a reasonably small battery and some extra help from the sun isn't a gamble that matters.

My definition of "sunshine when I need it" is a few hours every few days.

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sj_remington
 
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Re: Solar power for project

Post by sj_remington »

Ahh, so posting that question was a "bit of a joke".

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RandyPfeifer
 
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Re: Solar power for project

Post by RandyPfeifer »

No, the question was not a joke. The question I asked was "will connecting a solar panel in parallel with the charger component I referenced going to work (assuming sufficient sunlight)?".

A discussion on trusting sun (or not) isn't part of the question at all.

The response from Adafruit_support_bill was helpful.

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Rcayot
 
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Re: Solar power for project

Post by Rcayot »

Randy,

I am not a battery expert, but I have read that it is not wise to bundle lipos together. It is about them not being "matched" and one overcharging while the other gets finished.

Just what I read.

Rogwe

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RandyPfeifer
 
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Re: Solar power for project

Post by RandyPfeifer »

Oh thanks a ton. I'll definitely look into this. I was wondering if there might be a problem there...

Thanks again.

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adafruit_support_bill
 
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Re: Solar power for project

Post by adafruit_support_bill »

Rcayot is correct. It is not a good idea to wire lithium cells in parallel. Minor manufacturing variations between cells can lead to dangerous imbalances. Better to select a lhigher capacity cell, or a factory-assembled pack. Factory assembled packs are made from precision matched and balanced cells from the same manufacturing lot.

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RandyPfeifer
 
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Re: Solar power for project

Post by RandyPfeifer »

Hey, a follow-up on my little project. I bought a couple pieces of the USB/DS/Solar LiPo Charger and hooked one up this afternoon. When I got outside with the solar panel attached the green PGOOD and CHG lights light up as I would expect. I assume this means that output power is within spec and that the battery is being charged.

When I take the unit inside in the dark and plug it into the USB port on my laptop, the PGOOD light is on but the CHG light is not. This would seem to suggest that the battery is NOT being charged. Shouldn't it be charging the battery while on USB power?


what am I missing?

For completeness, the Load Out (and D+/-) are connected to an outgoing USB-C connector which powers my end gadget (and it's running fine). I'm charging a 650 mAh 3.7 v battery.

Oh and the battery is not charged yet...(I understand that the CHG light should go out when the battery is charged, right?)

Thanks in advance.

Randy

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adafruit_support_bill
 
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Re: Solar power for project

Post by adafruit_support_bill »

With the USB connected and the battery plugged in, what voltage do you see between the LiPo and GND pins?

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RandyPfeifer
 
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Re: Solar power for project

Post by RandyPfeifer »

I see a voltage that cycles between 3.7v and .5 v. over about 30 second period of time. up and down...

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adafruit_support_bill
 
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Re: Solar power for project

Post by adafruit_support_bill »

What is the voltage on the battery leads when you disconnect it from the circuit?

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RandyPfeifer
 
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Re: Solar power for project

Post by RandyPfeifer »

After sitting over night connected to the charger, I disconnected the battery and measure its voltage at 3.9V. When I plug it back into the charger with no power source connected (solar or usb), i measure the voltage at the battery connector at .3V. (load out same value).


But upon closer inspection of the connector on the board and the battery it seems that the pins are not aligned. The distance between the pins on the battery is much smaller. I'll bet the battery connection isn't proper. Image

The spec on the battery (per Amazon listing where I bought the battery) is "genuine JST Pitch1.25mm 2-pin connector module". Looks like the Adafruit JST is bigger....

I'll work on getting that fixed before drawing any further conclusions.
Last edited by RandyPfeifer on Sat May 07, 2022 10:12 am, edited 1 time in total.

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